A novel sulfur-emission free route for preparing ultrafine MoSi2 powder by silicothermic reduction of MoS2

The extraction of metal from sulfide mineral is usually accompanied by the emission of sulfur-containing gas (e.g., SO₂), which will cause serious pollution to the environment. In this work, a sulfur-emission free route for preparing ultrafine molybdenum disilicide (MoSi₂) powder by silicothermic reduction of MoS₂ with the desulfurization agent of lime was proposed. The internal MoS₂-Si mixture is wrapped in an external desulfurization layer composed of lime. After the reaction is completed, the prepared MoSi₂ can be easily separated from the desulfurization layer by using a non-chemical method. In addition, when the reaction temperature is higher than 1000°C, almost all S in MoS₂ is transformed to sulfur-containing gas SiS, which can be fully captured by lime to generate CaS, Si, and CaSiO₃. For the raw material with a MoS₂:Si molar ratio of 1:4, after reacting at 1000, 1100, and 1200°C for 2 h, the average grain sizes of the obtained MoSi₂ powder are approximately 100, 300, and 800 nm, respectively. Moreover, when the reaction time is prolonged from 2 to 6 h at 1000°C, the average grain size of the acquired MoSi₂ powder is about 200 nm, and the residual sulfur content is about 0.12%. This work provides a new insight to extract metals or metal compounds from sulfide ores without releasing sulfur-containing gas.